Optical measuring devices such as circular dichroism spectrometers, ultraviolet-visible spectrophotometers, and spectrofluorimeters are sometimes provided with cryostats for accommodating a cell. A cell accommodated in a cryostat is irradiated with a light beam to measure a spectrum, thereby allowing the chirality, structure, and the like of a compound to be determined (Non-patent Literature 1).
When an optical measurement is performed for a long period of time, there is a problem such that water vapor flows into the cryostat; consequently, water condenses on the surface of the cell, and the optical measurement cannot be performed effectively. In order to solve such a problem, operations for evacuating the cryostat and like operations have been conventionally performed.
However, in order to evacuate the cryostat, a special mechanism for maintaining vacuum or the like must be placed thereinside. Therefore, the internal structure becomes complicated, which is a cause of an increase in the size of cryostats.
Accordingly, the development of a cryostat that is small-sized and capable of effectively preventing water condensation on the surface of the cell has been strongly desired.
In addition, when the inside of the cryostat is under vacuum, optical windows may be distorted, and therefore the CD spectra cannot be accurately measured in some cases. Accordingly, the development of a cryostat with little distortion in optical windows even when the inside of the cryostat is under vacuum has been desired.